Teamwork Drives Turnkey Success
Suppliers team up to help power Ford's new F-150
By Jim Destefani
When engineers at Spartan Light Metal Products (Mexico, MO) were preparing a bid to design and manufacture cam covers used in 5.4-L V-8 engines for Ford's new F-150 pickup truck, expected part volumes and cycle times were the key concerns.
Developing a flexible, robust system to meet both current and future production and cost demands was also important, according to Director of Materials and Customer Service John Hunkins. "It's very competitive to get these kinds of programs," he says. "If you want the job, you get aggressive on your pricing up-front. Now we're already dealing with Ford's request for a price reduction, but we're in a much better position than we have been in the past. With the robustness built into this system, we have opportunities to make things better."
Founded in Sparta, IL in 1961, Spartan expanded by building the Mexico plant in 1995. The company is a magnesium and aluminum die caster that also specializes in production of cam, valve, and cylinder covers for automotive applications. Its customers include Ford, DaimlerChrysler, Honda, and Jaguar.
Still, Ford's volume demands meant that the F-150 cam cover system would be different than previous turnkey installations at the plant, says Engineering Manager Ralph Clendenin. "We have done several lines for Ford. The most important differences about this one are the throughput and speed of the line and the content that goes into the part.
"We had done quite a few assembly lines, including a fully palletized line, prior to this," he continues. "But the speed or volume that Ford needs for this is so high that we needed a new approach."
Cam covers for the 300-hp, three-valve-per-cylinder V-8 are produced from AZ91D magnesium die-casting alloy. They're currently shipped to engine assembly plants in Essex and Windsor, ON, and will also be shipped to Ford's Romeo, MI engine plant starting later this year. Volume was forecast to exceed 3600 sets per day.
The castings undergo multiple operations, including machining, gaging, washing, assembly, welding, and leak testing. Left- and right-hand cam covers vary slightly. The right-hand covers receive a fresh-air tube, while left-hand covers are machined to accept a PCV valve.
Assembly operations are complex. They include installation of the fresh-air tube or PCV valve assembly, a radial seal, a perimeter gasket, baffle plates for engine noise reduction, two U-drive studs, and mounting bolts with washers and spacers. All told, left-hand cover assemblies include 22 components. Right-hand covers use one less mounting bolt assembly and contain 20 parts.
Finding a machine vendor that could deliver a turnkey system to produce the covers was not easy, especially given the fact that Spartan's previous experience with turnkey systems had proved to be mixed. "This was our fifth real turnkey job," says Hunkins. "If you can't meet the operating performance assumptions used for the quote to your customer, then you don't meet the financial and customer satisfaction goals of the program. The payback is not there."
"The first thing we had to decide was how many parts we had to make," Clendenin says. From that, we come up with a cycle time. If we had a perfect process, with no fallout and no inefficiencies, cycle time would be 16 sec. However, we know that's not true."
Spartan specifies and approves equipment based on overall equipment effectiveness (OEE), a percentage obtained by multiplying availability, quality, and performance ratios. "On this line, we had to have 75% OEE, including scrap due to the castings that we provide," Clendenin says, "so we were looking at a cycle time of 11.5 sec. We also have some Spartan standards for machine building--for example, we always specify explosion-proof motors because we work with magnesium."
Other factors included the expected labor content needed to produce the parts. "One struggle was determining where operators would be on the line," Clendenin recalls. "There was a lot of discussion about exactly how that would work--the ergonomics, how much turning, twisting, and lifting we could expect, and how we could do that much work content and still not delay the line. With a cycle time of 11.5 sec, that was a challenge."
Spartan sought out a vendor that had experience in designing turnkey systems to produce parts at very fast cycle times, and eventually settled on Cincinnati Lamb Assembly and Test Systems (Rockford, IL). Cincinnati Lamb's Brian Ruhl became the liaison between Spartan's in-house team and the machine builder.
"The core team from Lamb's end was about seven people, and from Spartan the core team was at least five," Ruhl recalls. "We met several times in the proposal stage to make sure that what we were proposing was what Spartan really wanted. We had to compete against several other suppliers, and we were able to win the business."
The team approach served Spartan well not only in developing the system to manufacture Ford's cam covers, but in working with Ford design engineers and component vendors as well. "Being a full-service supplier means being involved in the design," Hunkins explains. "If you look at this part for the three-valve engine, and look at the component for the two-valve engine, it may not be a quantum leap. But each detail is appropriately matched for the needs of the engine."
"For example, a three-valve engine has different noise characteristics," Clendenin says. "So Ford asked us to design a system that was quiet, didn't leak, had the appropriate clearances, supplied the appropriate amount of PCV gas separation--and, the whole system had to be serviceable over a ten-year, 150,000-mile life. Those are the types of challenges that we're given."
Ford manages the development process through weekly team leader meetings. Clendenin explains that satisfying the needs of multiple Ford vehicle teams was one of the main challenges of part design. "The service folks need this, the PCV folks need this, the NVH [noise, vibration, and harshness] folks need this, and the assembly folks need another thing," he says.
By way of example, he points out small tabs on the casting that serve as a poka yoke for assembly of the engine's coil-on-plug ignition system. "There were many compromises on the outside, compromises on the inside--little nuances that are all over this thing."
One key design element that came out of the team meetings was a common datum scheme for manufacturing. "The B and C datums are absolutely mirrored between the left- and right-hand parts," Clendenin explains. "Keeping that the same had an incredible cost-saving impact to the line; it makes each of the fixtures absolutely identical."
Yet another example of teamwork in action was a redesign of the cover's perimeter gasket that resulted from a kaizen event with the gasket supplier. Prototype evaluation had shown that the gasket was relatively sensitive to casting variations.
"We called in [gasket vendor] Freudenberg NOK and Ford to participate on the kaizen team. In three days, we redesigned the perimeter seal to make it more robust," Hunkins recalls. "It was on the edge, and at these volumes we can't operate on the edge. As a result of the kaizen event, we changed the profile on the perimeter gasket to enable it to accept a rougher surface finish in the groove."
Clendenin explains that rough spots are inherent to the die-casting process. "The molten material wants to stick to the tool. It happens every day, and it's on a microscopic level. So we needed to design a sealing system that could deal with some roughness in the groove. We went from a seal design with one contact bead to a design with two contact beads, and redesigned some retention features."
Cam cover production begins when die-cast machine operators unload two parts--a left- and right-hand cover that are cast simultaneously. Operators perform a visual check for obvious casting defects, and use a simple handheld tool to check for debris or other problems with the gasket groove. Sample parts are inspected hourly for existing hole sizes, flatness, wall thickness, and other characteristics. Parts are then loaded directly onto the Lamb system's infeed conveyor.
At the other end, a Fanuc robot moves the casting to one of two six-station rotary transfer units for machining. "We selected rotary transfer machines because this particular product has some dedicated machining operations that didn't really require a CNC," Ruhl explains. "As fast as this system could run, we'd need five CNCs on the floor to match the output of one dial machine. Financially, that was a pretty easy decision to make--$2.5 million worth of CNCs versus an $800,000 dial machine." The two machining dials are identical, providing redundancy in the case of a problem with one unit.
Completed left-side cam cover assemblies consist of 22 parts, including mounting bolts, PCV valve, radial seal, U-drive studs, and perimeter gasket. Inset: the cover in place on Ford's 300-hp, 5.4-L Triton V-8 engine.
Either machine can process left- or right-hand covers in any order. Coil-on-plug holes are drilled and tapped four at a time on the first two machining stations. The third and fourth stations bore the hole for the fresh-air tube (right-hand covers, third station) or PCV tube (left-hand covers, fourth station). The fifth station machines the opening for the radial seal using a single head with dual spindles. The sixth station is currently used to flood parts with coolant to eliminate any stray chips that may be left on the parts.
After machining, the robot moves the parts to an in-process gaging system that performs 100% inspection on the radial seal ID and verifies thread presence in the holes used for mounting the engine's coil-on-plug units.
"Threads are a complete pass-through characteristic for us, so after this, we do hourly checks," explains Spartan Product Support Team Senior Engineer Matt Bridgman. "The customer is the first one to use them, and we don't like surprises. The radial seal we use a few minutes later, and we have load cell monitoring on that and 100% leak testing later." Tolerances on the machined features range from ±0.02 to ±0.035 mm.
A smaller Fanuc robot unloads the inline gage, deburrs the parts, and sends them to a carousel washer. At the first operator station, two U-drive studs are pressed in. "We use LVDTs and depth monitoring to verify depth and that there are no hole size problems," Bridgman explains. "For right-hand parts, we apply LocTite and press in the fresh-air tube. That operation is also monitored with load cells."
At the next station, the radial seal is pressed in. This operation is also monitored for load and depth, and the seal has to be oriented properly depending on whether the cover is a left- or right-hand.
At station three, the system applies LocTite to the PCV hole. An operator then inverts the cover and presses in the PCV valve. The process is monitored with load cells and for depth.
This is followed by manual loading of a steel baffle plate. After a check to assure that the baffle plate is properly located and fully seated, the plate is resistance-welded in place. "There are two heat-stake machines that attach the baffle plates by re-forming the heads on the bosses," Bridgman explains. "If for some reason those systems do not stake the part--for example, if one of the circuits went bad--there are faults, and the machine automatically rejects the part.
"That's the case with any station," he continues. "If it didn't make depth, if it didn't make pressure, if it didn't stake the baffle plate part for whatever reason, the system tags that part as a reject and it moves around the line to the reject station."
After heat staking, Station 6 turns the part over on the pallet, and prepares it for installation of the perimeter gasket. A pick-and-place unit pulls the part off the pallet, loads it onto a fixture, presses in the gasket, and puts it back on the pallet. At the next station parts are leak tested 100%.
Leak testing is one of several poka yokes built into the system. "If the gasket is missing or grossly misplaced, the part will be rejected. If the tube or radial seal is not there, the part won't seal and will be rejected. So the leak test is checking for the presence of all sealing components," Ruhl explains.
After leak testing, parts are released to one of four robots loading mounting bolts. A vision inspection station checks for the presence and position of all components. Parts that check OK are marked with a part number, date shipped, and serialized running identification, then released to either of two outbound conveyors--one each for left- and right-hand parts, which can't be mixed in dunnage--and packed for shipping.
Rejected parts are automatically unloaded at a reject station and marked in specific locations to help operators spot the problem. Operators inspect the rejects and either scrap them or send them to rework. "If a part, for example, failed the leak test, we'll disassemble all the components and retest it," Bridgman explains. "We can load reworked parts back on the line, and the system knows that that pallet contains a reworked part. If it fails again it's scrap."
Fitting the line into Spartan's roughly 80 X 40' (24 X 12 m) of available floor space proved to be a challenge. "We violated some of the standard rules that say, for example, you need to have three pallets in queue before every station for a nonsynchronous palletized line," Ruhl says. "But it works. Each station is set up so there are no bottlenecks on the line, and the operators work really well with the system so that bottlenecks have been avoided."
Spartan saved floor space by storing many components, including bolts, fresh-air tubes, and U-drive studs, above the line on a mezzanine. Perimeter gaskets and baffle plates are stored at the stations where they're used. Storage is not a small issue--for example, the line uses between 85,000 and 110,000 bolts per day.
The system had to complete a 40-hr run-off at Cincinnati Lamb, meeting the cycle time of 11.5 sec and the quoted OEE. "It had to produce at that level before it left Lamb," Clendenin says. "Can it produce at that level? Yes, it can. The current numbers approach 300 parts per hour."
This article was first published in the May 2004 edition of Manufacturing Engineering magazine.